Some disk drives are provided with a ramp (inclined) member, which is used to retract a head, near the outer periphery of the disk drive. It is desirable in such a disk drive to accurately control the head at a desired velocity on the ramp member, for example, in order to prevent the head from hitting a disk. Thus, conventionally, a torque exerted on a coil for driving the head is measured over the disk. Then, a torque when the head moves across the disk is corrected based on the measured torque. However, it is not clear in the correction method if the torque is corrected properly when the head moves on the ramp. This makes it difficult to accurately control the head at a desired velocity on the ramp.